Cardiopulmonary resuscitation (CPR) is a well known and valuable method of first aid. CPR is used to resuscitate people who have suffered from cardiac arrest after heart attack, electric shock, chest injury and many other causes. During cardiac arrest, the heart stops pumping blood, and a person suffering cardiac arrest will soon suffer brain damage from lack of blood supply to the brain. Thus, CPR requires repetitive chest compression to squeeze the heart and the thoracic cavity to pump blood through the body. Very often, the victim is not breathing, and mouth to mouth artificial respiration or a bag valve mask is used to supply air to the lungs while the chest compression pumps blood through the body.
It has been widely noted that CPR and chest compression can save cardiac arrest victims, especially when applied immediately after cardiac arrest. Chest compression requires that the person providing chest compression repetitively push down on the sternum of the victim at 80-100 compressions per minute. CPR and closed chest compression can be used anywhere, wherever the cardiac arrest victim is stricken. In the field away from the hospital, it may be accomplished by ill-trained by-standers or highly trained paramedics and ambulance personnel or at the hospital where it can be accomplished by doctors and nurses.
When a first aid provider performs chest compression well, blood flow in the body is typically about 25-30% of normal blood flow. This is enough blood flow to prevent brain damage. However, when chest compression is required for long periods of time, it is difficult if not impossible to maintain adequate compression of the heart and rib cage. Even experienced paramedics cannot maintain adequate chest compression for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, long periods of CPR, when required, are not often successful at sustaining or reviving the victim. At the same time, it appears that, if chest compression could be adequately maintained, cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended CPR efforts (45-90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
Mechanical devices for closed chest compression have been proposed and used. The device shown in Barkolow, Cardiopulmonary Resuscitator Massager Pad, U.S. Pat. No. 4,570,615 (Feb. 18, 1986), the commercially available thumper device, and other such devices, provide continuous automatic closed chest compression. However, these devices are not clinically more successful that manual chest compression. See Taylor, et al., External Cardiac Compression, A Randomized Comparison of Mechanical and Manual Techniques, 240 JAMA 644 (August 1978). Active compression decompression using a device which also lifts the chest wall after compression has been proposed. Stiel, et al., The Ontario Trial of Active Compression and Decompression Cardiopulmonary Resuscitation for In-Hospital and Prehospital Cardiac Arrest, 275 JAMA 1417 (1996) compared active compression-decompression with standard CPR, and found no significant improvement in survival or neurological outcome. A variety of other methods of increasing the effectiveness of CPR have been proposed, including abdominal binding and anti-shock pants. These techniques are intended to block blood flow to the abdomen and legs, thus directing blood flow to the brain. Again, these techniques have not proven effective in boosting the survival rate of cardiac arrest victims.
Chest compression must be accomplished vigorously if it is to be effective. Very little of the effort exerted in chest compression actually compresses the heart and large arteries of the thorax and most of the effort goes into deforming the chest and rib cage. The force needed to provide effective chest compression creates risk of other injuries. It is well known that placement of the hands over the sternum is required to avoid puncture of the heart during CPR. Numerous other injuries have been caused by chest compression. See Jones and Fletter, Complications After Cardiopulmonary Resuscitation, 12 AM. J. Emerg. Med. 687 (November 1994), which indicates that lacerations of the heart, coronary arteries, aortic aneurysm and rupture, fractured ribs, lung herniation, stomach and liver lacerations have been caused by CPR. Thus the risk of injury attendant to chest compression is high, and clearly may reduce the chances of survival of the victim vis-a-vis a resuscitation technique that could avoid those injuries. Also, chest compression will be completely ineffective for very large or obese cardiac arrest victims because the chest cannot be compressed enough to cause blood flow.
In the hospital setting, when closed chest compression is ineffective, doctors have the option of using open chest compression (also referred to as cardiac massage, open cardiac massage, open resuscitation, etc.). To accomplish open chest compression, the doctors perform a thoracotomy and pull the rib cage apart to open the chest, cut the heart out of the pericardial sac and expose the heart, and then "massage" the heart by hand (they squeeze it like a bladder pump). Mechanical devices for squeezing the heart during open chest surgery have been proposed, such as Goetz, Heart Massage Apparatus, U.S. Pat. No. 4,048,990, which provides a tulip shaped or basket-shaped bladder to surround the heart after the chest has been opened and the heart dissected from the pericardial sac. The grossly invasive thoracotomy procedure required for manual or mechanical open heart massage can only be accomplished in the hospital, and it carries its own risk of killing the cardiac arrest victim. Open chest cardiac massage is viewed as a last resort. See Blakeman, Open Cardiac Resuscitation, A Surgeons Viewpoint, 87 Postgraduate Med. 247 (January 1990). However, it has the benefit of increased blood flow compared to closed chest compressions, about 50% of normal blood flow. Bartlett, et al., Comparative Study Of Three Methods Of Resuscitation: Closed Chest, Open Chest Manual And Direct Mechanical Ventricular Assistance, 13 Ann. Emerg. Med. 773 (1984).
Direct cardiac massage can be accomplished without open heart surgery. Buckman, et al., Direct Cardiac Massage Without Major Thoracotomy, 29 Resuscitation 237 (1995) shows a cardiac compression device which has a small plate mounted on a handle, like a potato masher or a toilet plunger. The device is inserted through the chest wall, through an incision between the ribs which is 7.5 cm long. The device is placed so that the small plate is in contact with the left ventricle, then it is manually pushed against the heart to squeeze the heart. In both open cardiac massage and Buckman's minimally invasive direct cardiac massage, blood flow is accomplished by mechanically squeezing the heart so that it acts like a bladder pump.